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Sökning: L773:0435 3676 OR L773:1468 0459 > Refereegranskat

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1.
  • Linderson, Maj-Lena (författare)
  • Spatial distribution of meso-scale precipitation in Scania, southern Sweden
  • 2003
  • Ingår i: Geografiska Annaler. Series A. Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 85:2, s. 183-196
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study is to analyse the spatial variability of meso-scale precipitation in Scania and to assess the influence of synoptic scale atmospheric circulation. The modes of spatial variation are revealed by EOF analysis of monthly precipitation totals between 1963 and 1990, which were obtained from a dense rain-gauge network in Scania. southern Sweden. The influence of local physiography on the spatial distribution of precipitation is assessed by GIS techniques using a digital elevation model of Scania. The relation to synoptic scale atmospheric circulation is analysed using regional circulation indices and weather types. It is shown that the daily precipitation distribution in the area is significantly influenced by synoptic scale pressure patterns. Nevertheless. the covariability of the monthly precipitation within Scania is high. About 80% of the precipitation variability is connected to the passage of low-pressure centres over or close to the region. which are likely to produce precipitation over the whole area. A wind-direction dependency found in the distribution indicates that there might be a limit between precipitation regimes within the landscape. Topography greatly influences the spatial distribution in Scania. The distribution of land and surrounding sea is also an important factor and makes the relationship between physiography and precipitation rather complex. The physiographical effects vary over a single year. The dampening effect of the sea on the atmospheric temperature influences the local stability in coastal areas and results in seasonally dependent precipitation patterns.
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2.
  • Andresen, Camilla Snowman, et al. (författare)
  • Sholocene climate variability in the Denmark Strait region - A land-sea correlation of new and existing climate proxy records
  • 2005
  • Ingår i: Geografiska Annaler. Series A. Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 87:1, s. 159-174
  • Tidskriftsartikel (refereegranskat)abstract
    • Two well dated Holocene sediment records bordering the Denmark Strait region have been used to reconstruct past climate variability. The content of biogenic silica, clastic and organic material and moss in a lacustrine record from Lake N14 has been used to infer past variability in precipitation and temperature in southern Greenland. Sedimentologic and petrologic composition of sand in a shelf sediment record from the Djupall trough is used to infer past variability in the northwestern storm activity on northwestern Iceland, which probably also affected the inflow of polar waters from the East Greenland Current. Our evaluation of these records with a number of previous studies from the region documents Holocene climatic optimum conditions peaking between 8000 and 6500 calendar years before present (cal yr BP). Mid-Holocene climate deterioration set in around 5000 cal yr BP followed by a further marked setback around 3500 cal yr Bp. A stacking of climate variability on a centennial timescale from previous studies in the area shows a fairly good correspondence to the timing of marked cold and warm events as evidenced from the Lake N14 and the Djupull trough records. Cooler periods are explained as the response to marked incursions of ice-laden polar water from the Arctic Ocean to the Denmark Strait region. Cool northerly and northwesterly winds along the East Greenland coast in relation to frequent strong atmospheric low pressure in the Barents Sea, coupled with strong high pressure over Greenland, would have favoured southward export of polar waters. A comparison with the proxy records of nuclide production (C-14 and Be-10) suggests that solar activity may have had some influence on the atmospheric pressure distribution in the Denmark Strait region.
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3.
  • Håkansson, Lena, et al. (författare)
  • Cosmogenic Be-10-ages from the Store Koldewey island, NE Greenland
  • 2007
  • Ingår i: Geografiska Annaler. Series A. Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 89A:3, s. 195-202
  • Tidskriftsartikel (refereegranskat)abstract
    • Earlier work in northeast Greenland has suggested a limited advance of the Greenland Ice Sheet during the Last Glacial Maximum (LGM). However, this concept has recently been challenged by marine geological studies, indicating grounded ice on the continental shelf at this time. New Be-10-ages from the Store Koldewey island, northeast Greenland, suggest that unscoured mountain plateaus at the outer coast were covered at least partly by cold-based ice during the LGM. It is, however, still inconclusive whether this ice was dynamically connected to the Greenland Ice Sheet or not. Regardless of the LGM ice sheet extent, the Be-10 results from Store Koldewey add to a growing body of evidence suggesting considerable antiquity of crystalline unscoured terrain near present and Pleistocene ice sheet margins.
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4.
  • Ridefelt, Hanna, et al. (författare)
  • 56 years of solifluction measurements in the Abisko mountains, northern Sweden - analysis of temporal and spatial variations of slow soil surface movement
  • 2009
  • Ingår i: Geografiska Annaler. Series A. Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 91A:3, s. 215-232
  • Tidskriftsartikel (refereegranskat)abstract
    • Solifluction movement rates from 1952 to 2008 for the Abisko region, northern Sweden, have been compiled and analysed through correlation tests and multiple regression. The temporal analysis is based on two datasets (Lobe11 & gridAB and Line B) from Karkevagge. The dataset Lobe11 & gridAB show a strong correlation between movement rates and mean annual air temperature (MAAT) and MAAT is also identified as one of the significant contributing parameters in the multiple regression model. No significant correlations were found for the Line B dataset. The spatial analysis indicates generally higher movement rates in the western part of the region and at lower altitudes mainly between 700 and 900 m a.s.l., but the spatial variability is high. To reduce the influence of the temporal variation the data for the correlation tests of the spatial variations were divided into two parts: 1957 to 1980 and 1981 to 2008. The correlation analysis of the dataset 1957 to 1980 shows a significant negative correlation between annual average movement rates and permafrost probability and altitude. The dataset 1981 to 2008 shows a positive correlation between movement rates and wetness index. It is concluded that movement rates may increase with higher MAAT in the western part of the region (Karkevagge), the spatial variability of movement rates within the region is very high and that altitude (and/or permafrost) together with wetness index are the main controls on the regional spatial variation. The study highlights the limitations in establishing statistical relationships between movement rates and climate using data from different field empirical studies.
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5.
  • Yang, Zhenlin, et al. (författare)
  • Modelling Surface-Air-Temperature Variation Over Complex Terrain Around Abisko, Swedish Lapland: Uncertainties Of Measurements And Models At Different Scales
  • 2011
  • Ingår i: Geografiska Annaler. Series A. Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93A:2, s. 89-112
  • Tidskriftsartikel (refereegranskat)abstract
    • P>Many ecological, physical and geographical processes affected by climate in the natural environment are scale-dependent: determining surface-air-temperature distribution at a scale of tens to hundreds of metres can facilitate such research, which is currently hampered by the relative dearth of meteorological stations and complex surface temperature characteristics, particularly in mountain areas. Here we discuss both the couplings and mismatch of present climatological data at different scales, ranging from similar to 50 m to 100 km, and provide a novel model of the surface-air-temperature distribution in topographically heterogeneous regions. First, a comparison of the large-scale weather station measurements and gridded climate reanalysis (ERA-40) data is used to define regional climatology in the Swedish sub-Arctic and obtain the mesoscale temperature lapse rates. Second, combined with temperature measurements obtained from transects set among complex terrain, key microclimatic characteristics of the temperature distribution are identified, showing few temperature inversions when the wind speed exceeds 3 m s-1, while temperature inversions prevail during calm nights. Besides wind, there is a pronounced winter temperature stratification around the large Lake Tornetrask, and variations in topography are found to have a strong influence in shaping the microscale temperature pattern through their effect on solar radiation during summer. A monthly 50-m scale temperature-distribution (topoclimate) model is built based on the above findings, and model validation is conducted using further fieldwork measurements from different seasons. We present results of surface-air-temperature distribution for the Abisko region, and discuss how these results help reconcile the scale mismatch mentioned above.
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6.
  • Heyman, Jakob, et al. (författare)
  • Morphology, distribution and formation of relict marginal moraines in the Swedish mountains
  • 2006
  • Ingår i: Geografiska Annaler: Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 88A:4, s. 253-265
  • Tidskriftsartikel (refereegranskat)abstract
    • Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque-and-valley moraines, valley-side moraines, complex moraines and cross-valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice-sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice-sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation.
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7.
  • Beaudon, Emilie, et al. (författare)
  • Spatial and temporal variability of net accumulation from shallow cores from Vestfonna ice cap (Nordaustlandet, Svalbard)
  • 2011
  • Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 287-299
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyse ice cores from Vestfonna ice cap (Nordaustlandet, Svalbard). Oxygen isotopic measurements were made on three firn cores (6.0, 11.0 and 15.5 m deep) from the two highest summits of the glacier located on the SW–NE and NW–SE central ridges. Sub-annual δ18O cycles were preserved and could be counted visually in the uppermost parts of the cores, but deeper layers were affected by post-depositional smoothing. A pronounced δ18O minimum was found near the bottom of the three cores. We consider candidates for this δ18O signal to be a valuable reference horizon since it is also seen elsewhere in Nordaustlandet. We attribute it to isotopically depleted snow precipitation, which NCEP/NCAR reanalysis shows was unusual for Vestfonna, and came from northerly air during the cold winter of 1994/95. Finding the 1994/95 time marker allows establishment of a precise depth/age scale for the three cores. The derived annual accumulation rates indirectly fill a geographical gap in mass balance measurements and thus provide information on spatial and temporal variability of precipitation over the glacier for the period spanned by the cores (1992–2009). Comparing records at the two locations also reveals that the snow net accumulation at the easternmost part of Vestfonna was only half of that in the western part over the last 17 years.
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8.
  • Berglund, Mikael (författare)
  • The highest postglacial shore levels and glacio-isostatic uplift pattern in northern Sweden
  • 2012
  • Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Swedish Society for Anthropology and Geography. - 0435-3676 .- 1468-0459. ; 94:3, s. 321-337
  • Tidskriftsartikel (refereegranskat)abstract
    • The detailed clay varve chronology and an extensive knowledge of the highest postglacial shore level elevation (HS) in northern Sweden, along the Bothnian western coast, provides opportunities for determining the pattern of isostatic rise and centre of uplift from the early Holocene. The shore level of c. 10 100 cal yr bp (10 ka) for this area is determined by subtracting, from the metachronous HS elevations, the fall in relative sea level between local deglaciation time and the chosen reference time. The area of highest uplift since 10 ka is situated somewhat north of the location with the world-record HS (Skuleberget in Angermanland), but south of the area with most rapid current rise. Wave erosion marks in the studied area are seen to be more consistent indicators of HS than glaciofluvial delta levels. The gradients of shore marks at 10 ka are generally small within the investigation area. The regional 10 ka shore level pattern shows considerable irregularity compared to the current uplift. Central Sweden and western Finland show 10 ka gradients that indicate isostatic response to late (1310 ka bp) glacial unloading. Indications of a secondary uplift centre west of the present investigation area are reported in previous work; this also suggests rapid isostatic response to unloading. Finally, the possibility of identifying errors in the varve-dated deglaciation chronology via the 10 ka shore level pattern is illustrated.
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9.
  • Braun, Matthias, et al. (författare)
  • Changes of glacial front positions of Vestfonna (Nordaustlandet, Svalbard)
  • 2011
  • Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 301-310
  • Tidskriftsartikel (refereegranskat)abstract
    • Glaciers in Svalbard have shown considerable mass loss in recent years with a reported acceleration in the western and southern parts of the archipelago. However, for the ice cap Vestfonna, in northeastern Svalbard, climatic mass balance modelling has suggested almost balanced conditions over a period of nine years (2000–2009). A slightly positive geodetic mass balance (1990–2005) has been reported from a comparison of laser altimetry to older DEMs. A heterogeneous situation has been depicted for the various catchments, and hence changes in glacier extent can reveal additional information of glacier status, in particular when dealing with surge-type glaciers. We analysed a 34-year data record of multi-spectral satellite imagery in order to study changes in glacier frontal positions of the ice cap Vestfonna. A consistent pattern of almost steady retreat of the southern and north-eastern outlet glaciers of the ice cap is observed while Franklinbreen, the only major outlet glacier draining towards the north-west shows re-advance. This is consistent with an observed speed up and potential upcoming surge of this outlet. The glacier retreat on the southern coast also agrees with ICESat elevation change measurements. However, due to the glacier response time no direct relations between frontal retreat and surface mass balance can be drawn from the short observation period. The heterogeneous pattern of changes with on-going dynamic adjustments in some areas make the ice cap Vestfonna an ideal test site for future monitoring activities including novel techniques like differential interferometry from bi-static SAR systems.
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10.
  • Charpentier Ljungqvist, Fredrik, 1982- (författare)
  • A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia
  • 2010
  • Ingår i: Geografiska Annaler. Series A, Physical Geography. - Oxford : Wiley-Blackwell. - 0435-3676 .- 1468-0459. ; 92A:3, s. 339-351
  • Tidskriftsartikel (refereegranskat)abstract
    • A new temperature reconstruction with decadal resolution, covering the last two millennia, is presented for the extra-tropical Northern Hemisphere (90–30°N), utilizing many palaeotemperature proxy records never previously included in any large-scale temperature reconstruction. The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. AD 1–300, reaching up to the 1961–1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300–800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300–1900, followed by a rapid temperature increase in the twentieth century. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961–1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself. Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.
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